1. Field of the Invention
The present invention relates to a traveling vehicle system, particularly to a traveling vehicle system in which electric power is fed to the traveling vehicle using a contactless power feed arrangement.
2. Description of the Related Art
There is a known technology for a conveying vehicle configured to travel along a path for carrying articles in a clean room (e.g., in a semiconductor manufacturing plant), where dust production is a problem. An electric motor is typically used as a drive source for such a conveying vehicle. Electric power is supplied to the motor by electromagnetic induction from two power feed cables provided along the path of the conveying vehicle.
A method by which electromagnetic induction is utilized to conduct contactless power feeding will now be explained.
The two power feed cables are held in a power feed cable holder of a power feed rail provided along the path. A core that is made of ferrite and has a generally E-shaped cross sectional shape is fixed to an electric power receiving unit of the conveying vehicle. A coil is wounded onto a middle protruding piece of the core and the protruding piece is arranged between the two power feed cables such that it does not contact the power feed cables. When a high-frequency electric current is passed through the power feed cables, a magnetic field is generated and the magnetic field acts on the coil wound onto the core, causing an electric current to be induced in the coil. In this way, electric power is supplied from the power feed cables to the electric power receiving unit of the conveying vehicle in a contactless manner and the electric power is used by the motor and control devices (e.g., see Japanese Laid-open Patent Publication No. 2002-234366).
A semiconductor manufacturing plant has various apparatuses for processes such as inspection, exposure, impurity injection, etching, etc., and a traveling vehicle moves semiconductor wafers between loading ports of the processing apparatuses.
As explained above, the power feed cables used to supply electric power to the traveling vehicle system in a contactless manner generate a magnetic field and a portion of the magnetic field leaks to the outside from the power feed rail.
The inventor of the invention described and claimed in the present application, as set forth in more detail below, has discovered that there is a possibility that magnetic field leakage from the power feed rail will affect processing equipment used in a semiconductor manufacturing plant where the traveling vehicle system is used, particularly inspection equipment. For example, the inventor has discovered that when a semiconductor wafer having a line gap of 45 nm, for example, is inspected with a laser in an electron beam inspection apparatus, a magnetic field from the power feed cables sometimes affects a positioning function of the inspection apparatus and causes an incorrect measurement to occur. In particular, as semiconductor design rules progress toward smaller nodes, the problem of incorrect measurements becomes more of a concern.